| Recently,the intelligent Internet of Things(IoT)has developed rapidly with its increasing requirements for large-scale,multi-functional networks.Multi-channel integrated and independent sensors could connect the the user entity to the Internet by establishing a sensory information network,which could be applied to industrial production,environmental monitoring,human activities,etc.However,most of present sensors use external power supplies or traditional batteries.Large and complex power supply systems are becoming a bottleneck limiting their network development.An effective strategy to solve this problem is to establish a self-powered sensing system through energy storage or energy harvesting to enable the sensor to work independently for a long time.As an effective mechanical energy harvesting device,the output parameters of triboelectric nanogenerator(TENG),such as frequency and amplitude,could directly reflect external stimuli with high sensitivity.Considering that,TENG could perform as an active sensing device.However,this sensing system has limitations in material selection,environmental impact and external monitoring circuits.Therefore,originating from the intrinsic capacitance characteristic of TENG,an innovative self-powered sensing mechanism based on the resistive or capacitive impedance matching effect of TENG is established,which is the first study focus of this thesis.Introducing LED into the circuit,constructing self-powered quantitative display and alarm demonstration without external monitoring circuit,is the second focus of this thesis.The motion frequency of TENG is susceptible to external influence,especially in irregular motion environment.Based on the capacitive impedance matching effect,the self-powered sensing system is established,and its output is not affected by frequency fluctuations,greatly improving the reliability of the sensing system,which is the third key point of this thesis.Based on the above research points,this thesis explores the coupling effects between triboelectrification and external resistance/capacitance varition,and establishes the self-powered sensing application demonstration.The main research results are as follows:(1)Based on the resistive impedance matching effect of triboelectric nanogenerator and piezoresistive pressure sensor,we constructed a self-powered weighing system,containing three parts:a free-standing disc-shaped triboelectric nanogenerator(FD-TENG)as an energy harvester,a multi-walled carbon nanotube(MWCNT)-based piezoresistive pressure sensor as a weight sensor and some LEDs as warning lights.In the equivalent circuit model of TENG,the inherent capacitance is expressed as the impedance under the alternating voltage,and thus there is a matching resistor in the external circuit.The resistance changing range of the piezoresistive pressure sensor is within the resistance matching range of FD-TENG.Therefore,the output voltage of the sensor changes at different working status,which is directly reflected in the on/off state of LED.As a demonstration for practical application,the self-powered quality inspection system is built in a continuously operating crawler transport system to collect the mechanical energy wasted in the roller movement,and thus to power the piezoresistive pressure sensor,which could be utilized to detect qualified/unqualified industrial products.(2)A self-powered sensing mechanism based on the capacitive impedance matching effect of TENG is proposed.Since the internal impedance of a TENG is contributed by its inherent capacitance,there are different "capacitive impedance matching work areas".By connecting the TENG directly to the capacitive sensor,the capacitance of the sensor changes with the state of the external environment,and the electrical output signal changes accordingly.We explored the capacitive impedance matching effect of TENG under contact-separation and free-standing modes,and studied the effects of different working states on the "capacitive impedance matching work area".Self-powered pressure sensing model was initially established on the capacitive impedance matching effect of TENG.In addition,compared with resistive impedance matching effect induced self-powered sensing,the capacitive impedance matching effect induced self-powered sensing is not affected by the motion frequency,and the output signal remains constant at various motion frequencies,making it more suitable for human irregular motion(3)According to the coupling effect between triboelectrification of the TENG and capacitance variation of the sensor,a self-powered temperature sensing system is established.For a typical vertical contact-separation mode triboelectric nanogenerator(CS-TENG),when the external load capacitance in the circuit changes from 10 pF to 10 nF,the output voltage is reduced from?140 V to?5 V.The range can be considered as a capacitive impedance matching sensing range.Moreover,its output voltage characteristics maintain the same trend and value at various motion frequencies.That is to say,this self-powered sensing mechanism is not affected by the mechanical motion frequency and has high reliability and practicability,which is particularly suitable for all kinds of irregular motion.Based on this,we built a self-powered temperature sensing demonstratin,which combines a capacitive temperature sensor based on glycerol droplets with CS-TENG,and realizes quantifiable temperature sensing and high temperature alarm function through the working state of the LED. |
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